Sullivan. — The Winter- Flounder 129 



Figure 3. Stage 4 is two months old and shows the con- 

 dition at the end of metamorphosis. 



Stage 1 (Figure 1) . The length of the fish at hatching 

 is 3.5 mm. ; the greatest depth is 0.525. It is so translu- 

 cent as to become almost transparent when placed in a 

 glass dish. Only the pigment spots and the eyes are in 

 evidence. It can be studied most effectively at this time 

 by placing it against a white opaque background, that is, 

 by the use of a white-enameled dish. The group of dark 

 pigment spots shown on the posterior half of the body 

 is characteristic for this fish. The only other patch of 

 pigment of appreciable size lies over the rectum just pos- 

 terior to the yolk. As in most young fishes at this stage 

 the notochord, the digestive tract, the heart, the brain 

 and the auditory vesicle can be clearly seen. The noto- 

 chord is present as a straight tube. The dorsal, anal and 

 caudal fins are represented by an unbroken finfold. 



For several days after the hatching the external appear- 

 ance of the fish remains the same. The changes that one 

 observes first are the absorption of the yolk, the increase 

 in pigmentation and the modification of the finfold. The 

 even curves so conspicuous in the young stages become 

 replaced by angles and the appearance of the fish is al- 

 tered in consequence. The absorption of the yolk is very 

 gradual and the period involved varies with the water 

 temperature. At Woods Hole, where the average tem- 

 perature was 39.5 degrees Fahrenheit, it extended from 

 twelve to fourteen days. At Wickford with the higher 

 temperature the period was shortened perceptibly, never 

 extending over eight or nine days. The other processes of 

 development showed much the same relationship to the 

 water temperature, that is, in general the development is 

 much more rapid at the higher temperature. 



Stage 2 (Figure 2). The fish represented by Figure 2 

 is twelve days old. By this time it has reached a length 

 of 5 mm. The yolk is completely absorbed and the young 

 fish has come to depend entirely upon plankton for its 

 food. The boundaries of the finfold correspond very 

 closely to the boundaries of the fins of the adult, although 



